--- usr.sbin/cpucontrol/cpucontrol.8.orig
+++ usr.sbin/cpucontrol/cpucontrol.8
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd June 30, 2009
+.Dd January 5, 2018
 .Dt CPUCONTROL 8
 .Os
 .Sh NAME
@@ -36,44 +36,48 @@
 .Nm
 .Op Fl vh
 .Fl m Ar msr
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl vh
 .Fl m Ar msr Ns = Ns Ar value
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl vh
 .Fl m Ar msr Ns &= Ns Ar mask
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl vh
 .Fl m Ar msr Ns |= Ns Ar mask
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl vh
 .Fl i Ar level
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl vh
 .Fl i Ar level,level_type
-.Bk
 .Ar device
 .Ek
+.Bk
 .Nm
 .Op Fl vh
 .Op Fl d Ar datadir
 .Fl u
+.Ar device
+.Ek
 .Bk
+.Nm
+.Fl e
 .Ar device
 .Ek
 .Sh DESCRIPTION
@@ -129,6 +133,20 @@
 .Nm
 utility will walk through the configured data directories
 and apply all firmware updates available for this CPU.
+.It Fl e
+Re-evaluate the kernel flags indicating the present CPU features.
+This command is typically executed after a firmware update was applied
+which changes information reported by the
+.Dv CPUID
+instruction.
+.Pp
+.Bf -symbolic
+Only execute the
+.Fl e
+command after the microcode update was applied to all CPUs in the system.
+The kernel does not operate correctly if the features of processors are
+not identical.
+.Ef
 .It Fl v
 Increase the verbosity level.
 .It Fl h
--- usr.sbin/cpucontrol/cpucontrol.c.orig
+++ usr.sbin/cpucontrol/cpucontrol.c
@@ -60,6 +60,7 @@
 #define	FLAG_I	0x01
 #define	FLAG_M	0x02
 #define	FLAG_U	0x04
+#define	FLAG_E	0x10
 
 #define	OP_INVAL	0x00
 #define	OP_READ		0x01
@@ -114,7 +115,7 @@
 	if (name == NULL)
 		name = "cpuctl";
 	fprintf(stderr, "Usage: %s [-vh] [-d datadir] [-m msr[=value] | "
-	    "-i level | -i level,level_type | -u] device\n", name);
+	    "-i level | -i level,level_type | -e | -u] device\n", name);
 	exit(EX_USAGE);
 }
 
@@ -338,6 +339,25 @@
 }
 
 static int
+do_eval_cpu_features(const char *dev)
+{
+	int fd, error;
+
+	assert(dev != NULL);
+
+	fd = open(dev, O_RDWR);
+	if (fd < 0) {
+		WARN(0, "error opening %s for writing", dev);
+		return (1);
+	}
+	error = ioctl(fd, CPUCTL_EVAL_CPU_FEATURES, NULL);
+	if (error < 0)
+		WARN(0, "ioctl(%s, CPUCTL_EVAL_CPU_FEATURES)", dev);
+	close(fd);
+	return (error);
+}
+
+static int
 do_update(const char *dev)
 {
 	int fd;
@@ -431,11 +451,14 @@
 	 * Add all default data dirs to the list first.
 	 */
 	datadir_add(DEFAULT_DATADIR);
-	while ((c = getopt(argc, argv, "d:hi:m:uv")) != -1) {
+	while ((c = getopt(argc, argv, "d:ehi:m:uv")) != -1) {
 		switch (c) {
 		case 'd':
 			datadir_add(optarg);
 			break;
+		case 'e':
+			flags |= FLAG_E;
+			break;
 		case 'i':
 			flags |= FLAG_I;
 			cmdarg = optarg;
@@ -464,22 +487,25 @@
 		/* NOTREACHED */
 	}
 	dev = argv[0];
-	c = flags & (FLAG_I | FLAG_M | FLAG_U);
+	c = flags & (FLAG_E | FLAG_I | FLAG_M | FLAG_U);
 	switch (c) {
-		case FLAG_I:
-			if (strstr(cmdarg, ",") != NULL)
-				error = do_cpuid_count(cmdarg, dev);
-			else
-				error = do_cpuid(cmdarg, dev);
-			break;
-		case FLAG_M:
-			error = do_msr(cmdarg, dev);
-			break;
-		case FLAG_U:
-			error = do_update(dev);
-			break;
-		default:
-			usage();	/* Only one command can be selected. */
+	case FLAG_I:
+		if (strstr(cmdarg, ",") != NULL)
+			error = do_cpuid_count(cmdarg, dev);
+		else
+			error = do_cpuid(cmdarg, dev);
+		break;
+	case FLAG_M:
+		error = do_msr(cmdarg, dev);
+		break;
+	case FLAG_U:
+		error = do_update(dev);
+		break;
+	case FLAG_E:
+		error = do_eval_cpu_features(dev);
+		break;
+	default:
+		usage();	/* Only one command can be selected. */
 	}
 	SLIST_FREE(&datadirs, next, free);
 	return (error == 0 ? 0 : 1);